This application is an extension of R01-AR041880, funded by NIAMS. The funded study examines mechanisms that facilitate maturation of tyrosinase, the key catalytic enzyme required for melanin synthesis in melanocytes. The amount of melanin produced by melanocytes and subsequent skin pigmentation are dependent upon tyrosinase levels and activity. We have shown that when tyrosinase is retained in the endoplasmic reticulum (ER), as is the case in 3 genetically distinct forms of oculocutaneous albinism (OCA), the unfolded protein stress response (UPR) is activated. The resulting signal cascade, which has been implicated in the pathogenesis of type 1 diabetes, rheumatoid arthritis and some cancers, can trigger apoptosis. We have demonstrated that melanocytes can adapt to UPR activation, and Specific Aim 2 of our R01 investigates mechanisms underlying this adaptation. The ability of melanocytes to adapt to environmental assault is key to continued skin pigmentation and the resulting protection provided by melanin against ultraviolet light. Our preliminary data demonstrate that chemical agents that modulate the UPR alter the levels of melanin production in wildtype and albino melanocytes. In addition, the UPR is also activated in melanocytes by chemicals that trigger vitiligo, an acquired autoimmune disorder, and small molecules targeting UPR regulators can alter sensitivity to these toxins. Thus, developing a clear understanding of UPR activation in melanocytes may allow for the development of improved therapies for pigmentation disorders such as albinism and vitiligo. We have established a new collaboration that includes Drs. Orlow and Manga, the principal and co-investigator of the funded R01 respectively, and Dr. Timothy Cardozo, a pharmacologist and computational structural biologist specializing in drug discovery and molecular design. We propose to develop novel small molecules that modulate UPR activity by targeting specific proteins involved in the UPR signaling cascade. Dr. Cardozo has identified the first reported specific inhibitors of the key UPR regulator PERK. A similar approach will be used to develop small molecule inhibitors of UPR regulator IRE1alpha and GCN2, which shares targets with PERK. We will explore the effects of these novel inhibitors on melanocyte function and their utility in delineating the melanocyte UPR. Furthermore, we will assess their potential for use in the treatment of hyper and/or hypopigmentation as well as disorders of melanocyte viability such as vitiligo.